The invention relates to a transparent dental embedding material, a dental kit, a method for making a prosthesis, uses of the embedding material, a prosthesis, an individual flask, a dental pre-rim material. In dental technology a number of traditional methods are known for the production of prostheses.
In DE 195 02 751 A1 a method is disclosed for the production of plastic models for dentistry, in which a photosetting material is used.
GB 1,113,722 A describes an air-curing composition on the basis of mono or bis-acrylate or methacrylate monomers.
GB 916,075 A describes a method for preparing a cast composite article of polymerized methyl methacrylate resin.
In EP 0 142 172 A2 a polymerizable composition is disclosed which consists of a polar organic composition from the group of acids and their salts, a multifunctional vinyl crosslinking composition, and a solvent composition.
DE 36 39 067 A1 describes a method for making a dental plate in which photopolymerizing resins of different viscosities are used for direct formation within a short period of time of a dental plate in an appropriate manner with improved accuracy of fit, and the impression material used is a doughy product of photopolymerizing resins with different viscosities.
In DE 299 20 415 U1 a dental interspacing varnish is described which has a binding agent content of 5 to 60% of a polyvinyl alcohol, color pigments and a volatile alcohol miscible with water.
In the traditional method, on the one hand what is involved is the investment of a trial fitting in plaster of Paris in which the plaster of Paris is mixed with water and is poured over the trial fitting in a curette. After the plaster sets, the wax is boiled out and the plaster surfaces are isolated with alginate. The cavity formed can then be filled with thermally or chemically initiated plastic by the injection method, casting method or ramming method, and the material is polymerized by various methods. A disadvantage of this method is the relatively great expenditure of time and the fact that no visual control is possible to determine whether the flask has been completely filled. It is furthermore disadvantageous that no photopolymerizing materials can be used. In this process the plaster of Paris dries out with the attending changes in volume (shrinkage), while furthermore residual moisture in the plastic can cause discoloration of the plastic and in general a sealing with alginate is necessary.
Another method is the investment of the trial fitting in a hydrocolloid, wherein the hydrocolloid material, or also agar-agar, is liquefied by heating at temperatures above +50xc2x0 C. and then pouring it over the trial fitting in a flask. After the material has cooled and solidified the wax is removed and the cavity formed is filled with a 2-K autopolymer by the casting method. The 2 components of the autopolymer react by hardening onto the mixture and form the desired raw form of the prosthesis. A disadvantage of this method is the fact that this is a method that is error-prone, in which special flasks are necessary, and generally provides poor deflasking accuracy, and no polymerization is possible above 50xc2x0 C. It is a disadvantage that this method is suitable only for use with very fluid casting plastics, resulting in greater shrinkage after polymerization.
Lastly, the use of pre-rim silicone is known in partial prosthetic work such as completions in which silicone is modeled in the vestibule onto the trial fitting, cured on the corresponding model, and thus fixes the teeth in their position. Immediately thereafter casting plastic can be poured through the half-side opening and polymerized. A disadvantage in this process is the fact that the silicone has to be mixed from base and hardener, and wrong mixture ratios often result in defective hardening. Commercial condensation crosslinking silicones used for this purpose are transparent, but since they are tacky they cannot be mixed by hand.
Especially those silicones which crosslink by condensation are subject to shrinkage by losing water, and this can lead to prosthesis misfits. Furthermore, the time the silicones require for curing until they are usable is as much as 10 minutes, and furthermore the teeth must be fixed in the silicone by gluing with adhesives containing cyanoacrylate or wax.
From what is said above, the problem arises of how to overcome the above-named disadvantages by means of a novel dental investment material, a dental kit, a method for making a prosthesis, various uses of the investment material, as well as a prosthesis. The problem consists especially in designing a dental investment material which will assure optimum deflasking and accuracy of fit combined with advantageous material and handling properties.
This problem is solved according to the invention by a transparent investment material, a dental kit comprising this material, a method for making a prosthesis comprising this material, additional uses or prostheses made of this material, an individual flask having this material and a dental pre-rim material.
The dental investment material contains 10-30 weight-% polyethylene glycol dimethacrylate, 40-55 weight-% polymethyl methacrylate, 5-15 weight-% highly disperse silicon dioxide,  less than 1 weight-% photoinitiators, stabilizers, 0-10 weight-% polyethylene glycol and 10-30 weight-% of at least one compound from the group, urethane dimethacrylate, bis-GMA, and ethoxylated bis-GMA, and is highly transparent.
The investment material has optimum deflasking accuracy and accuracy of fit in setting up an individual flask, and the term, xe2x80x9cindividual flask,xe2x80x9d is to be understood as a cured dental investment material, especially a dental investment material according to the invention, which has been modeled over the work, including teeth, set up in wax. The cavity forming between the plaster of Paris base and the individual flask after removal of the wax can then be filled up with a commercial casting plastic. Due to the great transparency of the individual flask it is possible to use photopolymerizing material as the casting plastic.
The investment material according to the invention has a very high deflasking accuracy and fitting accuracy. Furthermore, the material has a certain elasticity, but on the other hand it is sufficiently brittle to permit easy removal of the individual flask or pre-rim by mechanically shattering the material.
In comparing the investment material of the invention with the known addition-crosslinking, transparent silicones (see DE 40 05 570 A1) the following is to be found: